Method and device for the in-situ formation of columns of stabilized and compacted soil

Abstract

The invention relates to civil engineering works. In particular, it relates to a device suitable for forming a primary column of stabilized and compacted soil, which comprises at least two parallel shafts driving in opposite directions, two parallel augers with opposite pitch, each auger being provided at the opposite end to the drive shaft with a loosening drillhead and the distance between the axes of the augers being less than the diameter of an auger, the shafts and the shanks of the augers comprising a bore connected to a source of material to be added, and at least one orifice which communicates with the said bore being provided on the shank of each auger so as to discharge the material to be added and allow it to be mixed with the loosened soil. Applicable in particular for the compaction of railroad territory.

I claim: 
     
       1. A method for the in-situ formation of a primary column of stabilized and compacted soil, comprising a first phase in which the ground is penetrated with a rotary drilling tool which loosens the soil and mixes it with an added material, and during which an ascending movement is imparted to at least some of the loosened soil through the drilling tool, and a second phase in which the drilling toll is withdrawn from the ground, wherein a descending movement is imparted to the loosened soil mixed with added material, through the drilling tool, by exerting a controlled pressure on the drilling tool during the said second phase, which descending movement tends to compact the said soil. 
     
     
       2. A method as claimed in claim 1, wherein the drilling and mixing operations of the first phase are repeated at least once. 
     
     
       3. A device for the formation of a primary column comprising at least two parallel shafts driving in rotation two parallel augers, each auger being provided at the opposite end to the drive shaft with a loosening drill-head, the distance between the axes of the augers being less than the diameter of an auger, the shafts and the shanks of the augers comprising a bore connected to a source of material to be added, and at least one orifice which communicates with the said bore being provided on the shank of each auger so as to discharge the material to be added allowing the added material to be mixed with the loosened soil, said augers having opposite pitches and being driven in rotation in opposite directions, said device including means for reversing the direction of rotation of the augers. 
     
     
       4. A device as claimed in claim 3, wherein the drilling head is in the form of a helix. 
     
     
       5. A device as claimed in claim 3, wherein the shafts and augers are kept parallel by means of double bearings. 
     
     
       6. A device according to claim 3, wherein the bore of one of said augers is connected to a source of a material to be added different from the material to be added of the source connected to the bore of the other auger.